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Testing if isolation has been effective

  • What happened?

    During a glycol aerial cooler cleaning campaign, the fan motors needed to be locked out so that workers could enter the fan cage to clean the fin tubes above the fan.

    Before doing this, the operator de-energized the breaker in the motor control centre and locked it in the open (energy off) position.

    Because the fans are controlled by the distributed control system, the control room operator tested they were isolated by attempting to start them remotely. The fans started – but they should not have been able to.

    The operator then tested for zero energy by putting the local switch to the ‘hand’ position and, again, the fan started.

    The fan was immediately shut down – if it had started up with the worker in the fan cage it could have caused severe injury or death.

    Demonstration of where the worker would have been located to conduct the work on the fan
  • Why did it happen?

    Upon investigation, it was found that the breaker knife switches were fused in the closed position.

    Demonstration of where the worker would have been located to conduct the work on the fan
  • What did they learn?

    Zero energy verification for all energy sources must be performed flawlessly before work begins.

    It is important to follow electrical energy isolation standards steps:

    1. Lock open breaker.
    2. Test ability to start at local switch.
    3. If tied to a distributed control system (DCS), put in a ‘run’ command.
    Electrical energy isolation standards
  • Ask yourself or your crew

    What could have happened if the work went ahead without the fan being isolated?

    How could something like this happen to us?

    How do we know that a fan (or other electrical equipment) has been isolated? How do we test it?

    What could we improve in how we ensure isolation of electrical equipment?

    Ask your crew - icon
Published on 17/04/24 543 Views

During a glycol aerial cleaning campaign, the fans started when they should not have, potentially causing severe injury or death to a worker. Upon investigation, it was found that the fan breaker knife switches were fused in the closed position.